Diesel fuel engine injection system and method therefor

ABSTRACT

Disclosed is a method of injecting LPG gas into a diesel fuel engine for combustion with diesel fuel therein. One aspect includes injecting LPG gas into an air-stream of an engine air intake or manifold, measuring the percentage of LPG gas injected into the airstream or other efficiency gauge, varying the rate of injection of LPG gas into the airstream in response to the measured percentage of LPG gas therein and injecting the LPG gas at a pre-determined rate so as to maintain an LPG gas concentration in the air intake stream in the range of 0.2% to 0.6% by volume of LPG gas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.12/066,033, filed Jun. 17, 2008, now U.S. Pat. No. 8,214,128 which is a371 of PCT International Application No. PCT/AU2007/001830, filed Nov.28, 2007, which claims priority from Australian Patent Application No.2007904436, filed Aug. 20, 2007 and Australian Patent Application No.2007906316, filed Nov. 20, 2007. U.S. patent application Ser. No.12/066,033 is incorporated herein by reference in its entirety as iffully set forth.

BACKGROUND OF THE INVENTION

Aspects of the invention relate to diesel fuel engines and to a methodand system for injecting LPG gas into a diesel fuel engine forcombustion therein.

Aspects have been developed primarily with respect to conventionaldiesel fuel engines and will be described hereinafter with reference tothis application. However, it will be appreciated that the invention isnot limited to this particular field of us and is also applicable tobio-diesel fuel engines, for example.

Diesel fuel engines are used widely in a large array of applicationssuch as transport, heavy machinery or power generation and form asignificant component of much equipment in agriculture, mining,construction, and freight and passenger transport. The recentsignificant rise in the price of diesel fuels has added to theimportance of maintaining diesel fuel engine equipment so as to allowthem to operate as efficiently as possible. Relatively small efficiencygains can lead to a dramatic decrease in fuel consumption and equipmentwear, together with corresponding reductions in pollution and otheremissions.

It is known that a combustible gas can be added to a diesel fuel engineair intake. The mixture of the combustible gas with the conventional airintake enhances combustion conditions within the cylinder so as toincrease efficiency of the diesel fuel combustion process. In the priorart, a combustible gas source, for example an LPG source, is connectedto an air inlet of a diesel fuel engine and injected by means of asolenoid valve, at some predetermined rate. This is drawn into theengine air intake stream and mixed in a venturi. The suction of theventuri is provided by the manifold vacuum or pressure difference.

Unfortunately, simple factors in engine performance deteriorationsignificantly reduce the efficiency of the combustible gas injection andhence engine combustion. For example, as the diesel engine is operated,its air filter will naturally reduce the flow rate it allows into theengine air intake streams. As a result, the level of the combustible gasinjected is not decreased proportionally. As a further result, the priorart start to decrease in any delivered efficiency gains and, dependingon the deterioration of engine components such as the air filter, can domore harm than good by providing conditions in which the engineefficiency is lower with a combustible gas injection than without.

One aspect provides a method and system of injecting LPG gas into adiesel fuel engine for combustion with diesel fuel therein which willovercome or substantially ameliorate one or more of the disadvantages ofthe prior art, or to provide a useful alternative.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided amethod of injecting LPG gas into a diesel fuel engine for combustionwith diesel fuel therein, the method including:

-   -   injecting LPG gas into an air-stream of an engine air intake or        manifold;    -   measuring the percentage of LPG gas injected into the airstream        or other efficiency gauge;    -   varying the rate of injection of LPG gas into the airstream in        response to the measured percentage of LPG gas therein and        injecting the LPG gas at a pre-determined rate so as to maintain        an LPG gas concentration in the air intake stream in the range        of 0.2% to 0.6% by volume of LPG gas.

According to a second aspect of the there is provided a method ofinjecting LPG gas into a diesel fuel engine for combustion with dieselfuel therein, the method including:

-   -   measuring engine revolutions per minute of the engine        (REVS_(current)) at predetermined revolutions from a minimum        value at engine idle (REVS_(min)) to a maximum value        (REVS_(max)) at wide open throttle;        measuring the load of the engine (Load_(current)) at        predetermined loads from an unloaded engine at idle (Load_(min))        through to a maximum loaded engine (Load_(max));    -   measuring an LPG gas flow rate of LPG gas into an airstream of        an engine air intake so as to maintain the percentage of LPG gas        mixed in the air intake to be in the range of 0.2% to 0.6% such        that a minimum gas injection rate (GAS_(min)) corresponds to an        idling engine under zero load.

According to a third aspect of the invention there is provided a systemfor injecting LPG gas into a diesel fuel engine for combustion withdiesel fuel therein, the system including:

-   -   an LPG gas injection device having an outlet disposed in fluid        communication with a diesel fuel engine air-inlet and an inlet        disposed in fluid communication with an LPG gas source;    -   an LPG gas injection device controller configured to receive        input indicative of an engine performance parameter and        configured to the control LPG gas injection rate from the LPG        gas injection device outlet such that the diesel engine        air-inlet has LPG gas injected therein to form an air-LPG gas        mixture having an LPG gas concentration of between 0.2% to 0.6%.

It can be seen there is provided a method and system of injecting LPGgas into a diesel fuel engine that improves combustion of diesel fuel inthe engine so as to decrease the emissions from the diesel engines. Themethod and system are also configured to be operable in response to oneor more of a variety of engine parameters and can be calibrated based onas little as two measured points.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 is a schematic representation of a circuit board of a deviceconfigured for injecting LPG gas into a diesel fuel engine according toa embodiment of the;

FIG. 2 is a connector pin description of the embodiment of FIG. 1;

FIG. 3 is a block circuit diagram of the system of FIG. 1;

FIG. 4 is a wiring diagram of the system of FIG. 1;

FIG. 5 is a harness diagram of the system of FIG. 1;

FIG. 6 is a table providing pin-out descriptions of the wiring andharness diagrams of the system of FIG. 1; and

FIG. 7 illustrates a look up table and corresponding determining formulafor gas injection rates of the system of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

According to an embodiment, there is disclosed a method and system ofinjecting LPG gas into a diesel fuel engine for combustion with dieselfuel in the engine. A diesel fuel engine is not illustrated.

The method includes injecting LPG gas into an air-stream of an engineair intake or directly into the manifold. The percentage of LPG gasinjected into the airstream is measured. The rate of injection of LPGgas (GAS_(inject)) into the airstream is responsive to the measuredpercentage of LPG gas in the airstream. This is to allow injection ofthe LPG gas at a pre-determined rate so as to maintain an LPG gasconcentration in the air intake stream in the range of 0.2% to 0.6% byvolume of LPG gas. Ideally, the LPG gas concentration in the air intakestream is maintained at substantially 0.35% by volume.

The LPG gas is injected into the airstream of the engine air intakeupstream of an engine cylinder inlet valve to provide best opportunityto mix the air and LPG gas. Measuring the percentage of LPG gas mixedinto the airstream of the engine intake includes bleeding a portion ofthe mixed LPG-air intake stream and sampling this directly with an LPGgas sensor. Alternatively, the LPG-air intake mixture can be measured bycombusting the bled LPG and measuring the products with a time delayedhot wire sensor. It will be appreciated that any preferred direct orsecondary LPG concentration sensor can be used as desired.

Alternatively, the air intake mixture of the engine can be measured bymeasuring the efficiency of the engine by using a nitrous oxide (NOx)sensor in the exhaust manifold, a temperature sensor in the exhaustmanifold or a gas sensor in the exhaust manifold.

The system uses the efficiency measurements to calculate LPG gas usagepoints and later extrapolates the required gas levels (GAS_(inject))from these stored points to provide a faster LPG gas injection responsetime that by direct sensor measurement of the LPG gas mixture in the airintake stream. In this alternative embodiment, the use of stored pointsderived from efficiency measurements can be replaced by calculating andstoring an electronic system map or table.

Operation of this method significantly improves the combustionefficiency of diesel fuel engines. This has the effects of reducingpollution and particulate matter, increasing power consumption andreducing fuel consumption.

Referring now to the embodiment illustrated in FIGS. 1 to 6, FIG. 1 is aschematic representation of a circuit board 10 of a device configuredfor injecting LPG gas into a diesel fuel engine so as to maintain an LPGgas concentration in the air intake stream in the range of 0.2% to 0.6%by volume of LPG gas. The circuit board 10 includes a connector 11configured to mate with a corresponding connector (not illustrated) forexample a DRC26-40, with 40 pins in the embodiment illustrated. FIG. 2is a connector pin description of the connector 11 of FIG. 1.

FIG. 3 illustrates a corresponding block circuit diagram of the system30 of the circuit board 10 of FIG. 1 indicating the device input side(31 to 38) into a microprocessor 39 and control (40) and communicationsdevice (41). A quad channel high side relay 40 receives control signalsfrom microprocessor 39 and sends a fuel enable signal to the output 40Ato allow gas flow. Two outputs 40B and 40C provide signals to controlthe flow of LPG gas into the air intake of the diesel fuel engine.

A communications device 41 in the form of a MAX3232CSE transceiverprovides an interface to the microprocessor 39. The system 30 isconfigured to receive inputs (31 to 36) in which the LPG gas temperaturebefore or after mixing with the air intake stream is measured by sensor31 in the form of a thermistor and sent to the microprocessor 39. Theengine speed or RPM is measured via an engine alternator sensor 32, theengine manifold pressure via sensor 34 and the exhaust temperature ismeasured by a thermocouple 33 having a cold junction compensatedthermocouple-digital converter 37 and EEPROM memory device 38 disposedintermediate the microprocessor 39.

An oxygen sensor 35 provides input into the microprocessor 39 indicatingthe oxygen levels of the air intake/LPG gas mixture. Switches 36 provideinput into microprocessor 39 to turn the LPG gas injection off when abrake pedal is depressed and/or the accelerator/throttle moved to a restor home position. The sensed parameters on the input side ofmicroprocessor 39 are indicative of the load and RPM of the engine. Thesystem 30 is also disabled when the engine ignition system is turnedoff.

A circuit wiring diagram for the connector 11 of the system of FIG. 1 isillustrated in FIG. 4. A corresponding harness diagram is illustrated inFIG. 5. In this Figure, the connector 11 is illustrated as connected tocomponents of the system. Data plug outputs 52, 53, 54 are provided,together with engine body earth connections 55, 56 and a means ofselecting a supply voltage 57. Fuses 58, 59 provide protection from thebattery and fuses 60, 61 protect an automatic gas shut off device. Aconnection to an exhaust gas temperature sensor 62, 63 is provided.

The connector 11 includes connections to control various system 30components (some not illustrated) such as the automatic gas shut offdevice positive and negative connections 64, 65 and a tachometer (RPM)pulse output 66. Control for four separate LPG gas injectors (notillustrated) is provided by outputs 67 to 74.

The connector 11 also includes a connection to a pressure switch signaloutput 75, 76, vehicle ignition output 77 and an MAP/TP sensor 78, 79,80. The connector 11 also includes LPG storage tank automated fuelshut-off device connections 81, 82, 83 and OEM and emulated MAP signalconnections 84, 85. The connector 11 outputs 86, 88 provide an LPG gasgauge connection and outputs 89,89 respectively provide a 12V switch andan LPG flow selector.

A connection to a throttle switch 90, 91 is provided via connection 11.Connections 92, 93 provide an output to an engine coolant temperature(ECT) sensor, and a measured propane sensor 94, 95, 96, 97 connection.

FIG. 6 presents a table providing pin-out descriptions of the wiring andharness diagrams of FIGS. 4 & 5. The circuit board 10 of the embodimentof FIG. 1 operating the system 30 illustrates various componentsincluding a connector 11, microprocessor 39, capacitors 110, 111, 112,123 having capacities of 0.1 μF, 10 μF, 1 μF and 470 μF respectively.High voltage capacitors 133 are also illustrated.

The circuit board 10 also schematically illustrates resistors 117, 119,124, 128, 129, 131 having capacities of 10 kΩ, 4.7 kΩ, 920Ω, 1 kΩ, 33 kΩand 100Ω respectively. Also illustrated are the following components:Zener diodes 113; voltage regulator 114; voltage relays 115, 116 thelatter being a quad channel high-side relay; diodes 118; communicationstransceiver 120 being a MAX3232CSE; under voltage sensing circuit 121;serial memory 122 as an 25LC1024 integrated circuit; a cold compensatedK-type thermocouple to digital converter 125; hex inverting Schmitttrigger 126; digital to analog converter 127; 5 A fuses 130; and RS 232communications port 132.

In the illustrated embodiment, the system for performing the method ofinjecting LPG gas into a diesel fuel engine includes an automated LPGfuel shut-off valve measured from a signal provided by an electricaloutput pulse from an engine regulator. In the absence of this electricalsignal, LPG valve is shut as the engine is not running. When calibratingthe system, the engine revolutions per minute of the engine(REVS_(current)) at predetermined revolutions from a minimum value atengine idle (REVS_(min)) to a maximum value (REVS_(max)) at wide openthrottle are measured and the corresponding LPG gas injection rate tomaintain 0.35% LPG gas of the volume of the air intake stream ismeasured.

The same step is repeated in respect of measuring the load of the engine(Load_(current)) at predetermined loads from an unloaded engine at idle(Load_(min)) through to a maximum loaded engine (Load_(max)) and againthe desired gas injection rate is measured. It will be appreciated thata minimum gas injection rate (GAS_(min)) corresponds to an idling engineunder zero load while maintaining a 0.35% LPG concentration in the airintake stream.

In the embodiment of FIGS. 1 to 6, the LPG gas injection rate(GAS_(inject)) is characterized for predetermined engine REVS(REVS_(current)) and load (Load_(current)) measurements storedelectronically as points of reference. In this embodiment, the value ofthe rate of LPG gas injection (GAS_(inject)) into the air intake streamis governed by the equation:

${GAS}_{inject} = {\begin{bmatrix}{\left\lbrack {\frac{1}{2}\begin{pmatrix}{\left( \frac{{Load}_{current} - {Load}_{m\; i\; n}}{{Load}_{{ma}\; x} - {Load}_{m\; i\; n}} \right) +} \\\left( \frac{{REVS}_{current} - {REVS}_{m\; i\; n}}{{REVS}_{{ma}\; x} - {REVS}_{m\; i\; n}} \right)\end{pmatrix}} \right\rbrack*} \\\left( {{GAS}_{{ma}\; x} - {GAS}_{m\; i\; n}} \right)\end{bmatrix} + {GAS}_{{m\; i\; n}\;}}$

In this equation, GAS_(max) is the required gas injection rate undermaximum engine REVS and maximum Load and GAS_(min) is the gas injectionrate under minimum engine REVS and minimum or zero Load.

The engine REVS is determined by means of a measurement of the output ofthe diesel fuel engine alternator or other engine signal source. Thisprovides a signal directly proportional to engine REVS. The diesel fuelengine load (Load_(current)) is measured via a corresponding measurementof manifold absolute pressure sensor. The sensor output is directlyproportional to the engine load.

However, it will be appreciated that the engine REVS can be measured byany other preferred means and that the engine load may also be measuredby other means such as by an engine turbo charger pressure sensor, anexhaust temperature sensor, throttle positioning sensor and/or anexhaust nitrous-oxide gas sensor, for example. Furthermore, the aboveequation can be modified to characterize the desired gas injection rateaccordingly.

FIG. 7 illustrates a look up table of LPG gas injection rates as afunction of engine REVS and Loads. The look up table is characterized bythe above equation. For an idling engine under zero or minimum load (andminimum REVS), the injected LPG gas rate corresponds to GAS_(min). Thisoccurs also in response to a signal from a throttle switch whichindicates deceleration, braking and/or an idle condition. In a likemanner, the LPG injection system is disabling in response to a signalfrom an LPG tank sensor indicating exhaustion of the LPG.

In this embodiment, it will be appreciated that the system can becalibrated or re-calibrated as desired by measuring the required gasinjection rates over the load and REVS ranges so as to maintain a 0.35%volume of LPG gas concentration in the air intake stream and storingthese rate values in a look up table accordingly.

In the embodiment of FIGS. 1 to 6, it will be appreciated that systeminputs corresponding to manifold pressure, engine REVS, etc. areconnected to the apparatus of FIG. 1. This apparatus has output tocontrol both the supply of LPG gas but also the rate of injectionthereof into the air intake stream.

It will be appreciated that the embodiments of the present invention isadvanced over the prior art for at least important reasons. Firstly, thepresent invention can be “auto-tuned” by use of a third variable againstengine REVS and load to determine the correct rate of gas injection tomaintain the air intake volume with 0.35% LPG gas. It will be furtherappreciated that LPG gas can be substituted with any preferredcombustible gas such hydrogen, natural gas or other flammable gas. Thethird variable measured in the embodiments of the present invention isthe percentage LPG gas in the air intake volume, however, diesel flow,air flow, NOx, oxygen or temperature may all suitably be used as thethird variable.

Once the three variables are known, the correct gas injection rates canbe generated and a map or reference points also generated.

The second advantage over the prior art is the use of the above gasinjection equation. Instead of necessarily using a system map or tablecontaining possibly hundreds of points, two points are stored (idle andanother point which is greater than idle) and the gas injection rate iscalculated using the above equation. The advantage of this is insteadapplying relatively significant time to measure all these hundreds ofvalues, the present invention requires the measurement of just two. Theuse of a model equation is also more accurate than using a look-up tablebecause it can calculate the exact value instead of picking the closestpoint on the map.

For example, it will be appreciated that if LPG usage was sinusoidalthen the above equation would also be sinusoidal and a map would be asquare wave. Also, although in the embodiment the gas LPG injected intothe air intake stream is sampled using a propane sensor, injectiondirectly into the manifold can be provided and the level of LPG gas inthe air intake stream is measured using testing the NOx levels in theexhaust. Of course, hydrogen or aquagen, for example, could be injectedinto the diesel engine manifold and the NOx levels measured in theexhaust to determine the correct gas injection rates. Such a system isenvisaged for water to be used instead of LPG for fuel.

It will be appreciated that in other embodiments of the invention, notillustrated, that the LPG gas injection rate (GAS_(inject)) ischaracterized for predetermined engine REVS (REVS_(current)) and load(LOAD_(current)) measurements stored electronically as points ofreference. In alternative embodiments, the rate of LPG gas injection(GAS_(inject)) into the intake stream is governed by the equation:

${GAS}_{inject} = {\begin{bmatrix}{\left\lbrack \begin{pmatrix}{{N\left( \frac{{Load}_{current} - {Load}_{m\; i\; n}}{{Load}_{m\;{ax}} - {Load}_{m\; i\; n}} \right)} +} \\{M\left( \frac{{REVS}_{current} - {REVS}_{m\; i\; n}}{{REVS}_{m\;{ax}} - {REVS}_{m\; i\; n}} \right)}\end{pmatrix} \right\rbrack*} \\\left( {{GAS}_{{ma}\; x} - {GAS}_{m\; i\; n}} \right)\end{bmatrix} + {GAS}_{m\; i\; n}}$

In this governing equation, the variables N and M are positive andsatisfy the equation N+M=1. In this way, the relative contributions tothe GAS_(inject) can be predetermined as preferred for each of N and Mbeing 0 or greater but not greater than 1. The weightings N and M arechosen depending on preferences, for example, N=0.4 and M=0.6 in thecase of a standard turbo diesel vehicle engine. In this way, theGAS_(inject) rate is more heavily weighted upon the engine revolutionsthan the engine load. In a naturally aspirated diesel engine, N can=0and M can=1 so that the component of measured load is not considered inthe determination of the gas injection rate GAS_(inject). In the case ofa stationary diesel engine, it is preferred that only engine load ismeasured and so N=1 and M=0.

It will be appreciated that any preferred values for N and M can beprovided so long as N+M=1. As noted above, it will be appreciated thatthe equation which combines weightings of measured REVS and load valuescan be used in the same manner as the embodiment described. That is, thegas injection rate to provide 0.35% concentration of LPG gas in theair-intake can be governed by the use of an equation in which the loadand revolution measurements are weighted depending on the engine andapplication.

As is described herein, the injection of LPG gas into the air-inlet of adiesel fuel engine can be provided in concentrations of between 0.2% to0.6%. When a concentration of 0.6%, for example, is provided the dieselengine power performance is not improved, however, significantly feweremissions are generated. The typical diesel engine particulate matteremissions are significantly reduced as compared to when no LPG gasinjection is provided. When an LPG concentration at the diesel engineair-intake is 0.35%, for example, then not only are emissionssignificantly reduced, but the power output of the engine is alsoincreased.

As noted above, the flammable gas injection rates are switched to theminimum gas injection rate (GAS_(min)) responsive to the signal from thethrottle position switch. This indicates deceleration, braking and/or anidle position. When the throttle position switch is moved into the offposition and no fuel is injected into the engine corresponding to anidle condition the present system 1 substantially instantaneouslyreduces the gas injection rate (GAS_(min)) to zero. If gas was beinginjected on deceleration it would go straight through the engineunburned and would create a hydrocarbon spike in the exhaust. This issince most modern diesel engines are electronically controlled and cutthe diesel injection on deceleration and the gas injected in the presentinvention relies on combustion of the diesel fuel to be enhanced in thepresence of the inject flammable gas.

It is also noted that on trucks that have exhaust or engine brakes thatare engageable upon deceleration, these can have significant boostpressure in the inlet manifold during operation. If the flammable gaswere injected, it may be a sufficiently high percentage to allow abuild-up of the unburnt flammable gas in the exhaust. When accelerationis resumed unburned gas in the exhaust can be ignited upon combustion ofthe diesel fuel causing an exhaust fire or engine explosion. This riskis minimized in the present invention as the flammable gas injected isto enhance combustion of the diesel fuel and not to act as a primaryfuel source.

The use of the throttle switch is hitherto unknown and advantageous inthe preferred embodiments of the invention because most modern dieselfuel engines are now electronically controlled and have cruise controlwhich means the throttle remains at rest and no gas injection occurs sothat minor programming of the apparatus of FIG. 1 can be used to receiveinput providing an indication between the difference in decelerationaction of the engine and cruise control operation. That is, moderndiesel engines are electronically controlled and a direct cableconnection between the throttle pedal and the engine is no longertypically provided. As such, use of a cruise control on a modern dieselengine does not result in corresponding movement of the throttleposition. As such, the throttle position sensor measurements on its owncannot distinguish between operation of the cruise control and adeceleration. In the present system, when the throttle position is movedto zero GAS_(min) is injected as above corresponding to the minimum loadand revolutions of the engine. If after a predetermined period of time,for example one minute in the present invention, then the system 1considers that the cruise control is in operation and that decelerationis not in action and the GAS_(inject) rate is returned to provide 0.35%of the air intake volume of flammable gas.

The foregoing describes only one embodiment of the present invention andmodifications, obvious to those skilled in the art, can be made theretowithout departing from the scope of the present invention.

The term “comprising” (and its grammatical variations) as used herein isused in the inclusive sense of “including” or “having” and not in theexclusive sense of “consisting only of”.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

While the principles of the invention have been described above inconnection with preferred embodiments, it is to be clearly understoodthat this description is made only by way of example and not as alimitation of the scope of the invention.

The invention claimed is:
 1. A method of injecting flammable gas into adiesel fuel engine for combustion with diesel fuel therein, the methodcomprising: measuring engine revolutions per minute of the engine(REVS_(current)) at predetermined revolutions from a minimum value atengine idle (REVS_(min)) to a maximum value (REVS_(max)) at wide openthrottle; measuring the load of the engine (Load_(current)) atpredetermined loads from an unloaded engine at idle (Load_(min)) throughto a maximum loaded engine (Load_(max)); measuring a flammable gas flowrate of flammable gas that is injected into an airstream of an engineair intake so as to maintain the percentage of flammable gas mixed inthe air intake to be in the range of 0.2% to 0.6% such that a minimumgas injection rate (GAS_(min)) corresponds to an idling engine underzero load.
 2. The method of claim 1 further comprising measuring theefficiency of the engine at idle (REVS_(min)) and again under load anddetermining the correct rate of gas to inject (GAS_(inject)).
 3. Amethod of claim 1, wherein injecting the flammable gas is governed bythe equation: ${GAS}_{inject} = {\begin{bmatrix}{\left\lbrack {\frac{1}{2}\begin{pmatrix}{\left( \frac{{Load}_{current} - {Load}_{m\; i\; n}}{{Load}_{{ma}\; x} - {Load}_{m\; i\; n}} \right) +} \\{M\left( \frac{{REVS}_{current} - {REVS}_{m\; i\; n}}{{REVS}_{m\;{ax}} - {REVS}_{m\; i\; n}} \right)}\end{pmatrix}} \right\rbrack*} \\\left( {{GAS}_{m\;{ax}} - {GAS}_{m\; i\; n}} \right)\end{bmatrix} + {GAS}_{m\; i\; n}}$ where GAS_(max) is the gas injectionrate under maximum engine REVS and maximum Load; and GAS_(min) is thegas injection rate under minimum engine REVS and minimum Load.
 4. Themethod of claim 1, wherein injecting the flammable gas is governed bythe equation: ${GAS}_{inject} = {\begin{bmatrix}{\left\lbrack \begin{pmatrix}{{N\left( \frac{{Load}_{current} - {Load}_{m\; i\; n}}{{Load}_{{ma}\; x} - {Load}_{m\; i\; n}} \right)} +} \\{M\left( \frac{{REVS}_{current} - {REVS}_{m\; i\; n}}{{REVS}_{m\;{ax}} - {REVS}_{m\; i\; n}} \right)}\end{pmatrix} \right\rbrack*} \\\left( {{GAS}_{m\;{ax}} - {GAS}_{m\; i\; n}} \right)\end{bmatrix} + {GAS}_{m\; i\; n}}$ where GAS_(max) is the gas injectionrate under maximum engine REVS and maximum Load; GAS_(min) is the gasinjection rate under minimum engine REVS and minimum Load; and N and Mare positive and satisfy the equation N+M=1.
 5. The method of claim 1,wherein injecting the flammable gas is governed by the equation:${GAS}_{inject} = {\left\lbrack {\left\lbrack \left( {{0.4\left( \frac{{Load}_{current} - {Load}_{\min}}{{Load}_{\max} - {Load}_{\min}} \right)} + {0.6\left( \frac{{REVS}_{current} - {REVS}_{\min}}{{REVS}_{\max} - {REVS}_{\min}} \right)}} \right) \right\rbrack*\left( {{GAS}_{\max} - {GAS}_{\min}} \right)} \right\rbrack + {GAS}_{\min}}$where GAS_(max) is the gas injection rate under maximum engine Load; andGAS_(min) is the gas injection rate under minimum engine Load.
 6. Themethod of claim 1, wherein injecting the flammable gas is governed bythe equation:${GAS}_{inject} = {\left\lbrack {\left\lbrack \left( \left( \frac{{Load}_{current} - {Load}_{\min}}{{Load}_{\max} - {Load}_{\min}} \right) \right) \right\rbrack*\left( {{GAS}_{\max} - {GAS}_{\min}} \right)} \right\rbrack + {GAS}_{\min}}$where GAS_(max) is the gas injection rate under engine Load; andGAS_(min) is the gas injection rate under minimum engine Load.
 7. Themethod of claim 1, wherein injecting the flammable gas is governed bythe equation:${GAS}_{inject} = {\left\lbrack {\left\lbrack \left( \left( \frac{{REVS}_{current} - {REVS}_{\min}}{{REVS}_{\max} - {REVS}_{\min}} \right) \right) \right\rbrack*\left( {{GAS}_{\max} - {GAS}_{\min}} \right)} \right\rbrack + {GAS}_{\min}}$where GAS_(max) is the gas injection rate under maximum engine REVS; andGAS_(min) is the gas injection rate under minimum engine REVS.
 8. Themethod of claim 3, wherein the flammable gas injection rate(GAS_(inject)) rate, is characterised by measuring GAS_(inject) for theengine under maximum load and maximum engine REVS (GAS_(max)) and forthe engine under zero load at idle (REVS_(min)) (GAS_(min)) andextrapolating therebetween by means of the equation.
 9. The method ofclaim 6, wherein the flammable gas injection rate (GAS_(inject)) rate,is characterised by measuring GAS_(inject) for the engine under maximumload (GAS_(max)) and for the engine under zero load (GAS_(min)) andextrapolating therebetween by means of the equation.
 10. The method ofclaim 7, wherein the flammable gas injection rate (GAS_(inject)) rate,is characterised by measuring GAS_(inject) for the engine under maximumengine REVS (GAS_(max)) and for the engine at idle (REVS_(min))(GAS_(min)) and extrapolating therebetween by means of the equation. 11.The method of claim 1, wherein the diesel fuel engine load(Load_(current)) is measured via a corresponding measurement of amanifold absolute pressure sensor, a turbo charger pressure sensor,throttle positioning sensor, an exhaust temperature sensor, and/or anexhaust nitrous-oxide gas sensor, or by attaching the engine to adynameter; and wherein the engine REV. rate is measured via the voltageoutput of the diesel fuel engine alternator or other engine signalsource.
 12. The method of claim 1 comprising switching injectedflammable gas rates to the minimum gas injection rate (GAS_(min)) inresponse to a signal from a throttle switch thereby indicatingdeceleration, braking and/or idle condition.
 13. The method claim 1comprising re-performing the steps of the method of claim 1 atpredetermined times to recalibrate the flammable gas injection rate(GAS_(inject)) and resetting the flammable gas injection ratecorrespondingly.
 14. A system for injecting flammable gas into a dieselfuel engine for combustion with diesel fuel therein, the systemcomprising: a flammable gas injection device having an outlet disposedin fluid communication with a diesel fuel engine air-inlet and an inletdisposed in fluid communication with a flammable gas source; and aflammable gas injection device controller configured to receive inputindicative of an engine performance parameter and configured to thecontrol flammable gas injection rate from the flammable gas injectiondevice outlet such that the diesel engine air-inlet has flammable gasinjected therein to form an air-flammable gas mixture having a flammablegas concentration of between 0.2% to 0.6%.
 15. The system of claim 14,wherein the engine performance parameter includes a percentage offlammable gas mixed into the airstream of the engine intake; enginerevolutions per minute of the engine (REVS_(current)) at predeterminedrevolutions from a minimum value at engine idle (REVS_(min)) to amaximum value (REVS_(max)) at wide open throttle; a load of the engine(Load_(current)) at predetermined loads from an unloaded engine at idle(Load_(min)) through to a maximum loaded engine (Load_(max)); a voltageoutput of the diesel fuel engine alternator or other engine signalsource; and manifold absolute pressure, a turbo charger pressure,throttle position, exhaust temperature, and/or an exhaust nitrous-oxidegas, or an engine dynameter.
 16. The system of claim 14, wherein theflammable gas injection device controller is configured to operate theequation: ${GAS}_{inject} = {\begin{bmatrix}{\left\lbrack \begin{pmatrix}{{N\left( \frac{{Load}_{current} - {Load}_{m\; i\; n}}{{Load}_{{ma}\; x} - {Load}_{m\; i\; n}} \right)} +} \\{M\left( \frac{{REVS}_{current} - {REVS}_{m\; i\; n}}{{REVS}_{{ma}\; x} - {REVS}_{m\; i\; n}} \right)}\end{pmatrix} \right\rbrack*} \\\left( {{GAS}_{{ma}\; x} - {GAS}_{m\; i\; n}} \right)\end{bmatrix} + {GAS}_{m\; i\; n}}$ where GAS_(max) is the gas injectionrate under maximum engine REVS and maximum Load; GAS_(min) is the gasinjection rate under minimum engine REVS and minimum Load; and N and Mare positive and satisfy the equation N+M=1.
 17. The system of claim 16,wherein the flammable gas injection device controller is configured toprovide a flammable gas injection rate into the air-inlet (GAS_(inject))at a rate characterised by measuring GAS_(inject) for the engine undermaximum load and maximum engine REVS (GAS_(max)) and for the engineunder zero load at idle (REVS_(min)) (GAS_(min)) and extrapolatingtherebetween by means of the equation.
 18. A diesel fuel enginecomprising: a flammable gas injection device having an outlet disposedin fluid communication with a diesel fuel engine air-inlet and an inletdisposed in fluid communication with a flammable gas source; and aflammable gas injection device controller configured to receive inputindicative of an engine performance parameter and configured to thecontrol flammable gas injection rate from the flammable gas injectiondevice outlet such that the diesel engine air-inlet has flammable gasinjected therein to form an air-flammable gas mixture having a flammablegas concentration of between 0.2% to 0.6%.
 19. The method of claim 14wherein the flammable gas injection rate (GAS_(inject)) rate ischaracterised by measuring GAS inject for the engine under maximum loadand maximum engine REVS (GAS_(max)) and for the engine under zero loadat idle (REVS_(min)) (GAS_(min)) and extrapolating therebetween by meansof the equation.
 20. The method of claim 15 wherein the flammable gasinjection rate (GAS_(inject)) rate, is characterised by measuring GASinject for the engine under maximum load and maximum engine REVS(GAS_(max)) and for the engine under zero load at idle (REVS_(min))(GAS_(min)) and extrapolating therebetween by means of the equation. 21.The system of claim 14 where the flammable gas is LPG gas, hydrogen gas,natural gas or other flammable gas.